The field of the disclosure relates generally to electric motor control systems, and more particularly, to motor controllers including high-frequency inverters and filter systems to reduce bearing currents induced in electric motors.
In some electric motors using pulse width modulation (PWM) type inverters, a common mode voltage is induced on a motor shaft by switching behavior of semiconductor devices in the inverter. This common mode voltage results in a potential difference across the motor and ground that produces a current that may flow through the motor bearings, i.e., a bearing current. The bearing current reduces a useable lifetime of the bearings and can lead to significant bearing damage. The magnitude of the bearing current is a function of fluctuations or spikes on a waveform generated by an inverter in the motor's control system to drive the motor.
Bearing current may be reduced by mechanical design features, such as grounding brushes. These carbon fiber brushes are disposed in a ring about the bearing surface and create a short-circuit path any induced bearing voltage. However, such grounding brushes increase a total common mode current to ground, which leads to increased electromagnetic interference (EMI) in the motor electronics. Accordingly, a solution for reducing bearing current while also minimizing EMI would be desirable.